Performance of recycled paper mill sludge as a modifier in sphalt mixtures through dry process
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Date
2018-08-01
Authors
Chew J-Wei
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Abstract
The escalating accretion of solid waste requires a global notion to strive for
efficient waste management and ecological treatments. The asphalt pavement
industry which consumes natural resources while contributing to greenhouse
emissions, is viewed as a potential alternative for the incorporation of solid waste.
This research effort incorporates Recycled Paper Mill Sludge (RPMS) as a solid
waste addictive into asphalt mixture. Pre-requisite treatment of RPMS required 6
hours oven dried, 10 cycles milling and sieved retaining 0.075mm while found to be
not combustible. Over 60% RPMS is utilized, while remaining 40% can be utilized
as soil amendments. RPMS is incorporated into asphalt mixture at 0.5% and 1%
asphalt mixture weight. Asphalt binder with penetration grade 60/70 and two types of
aggregates namely limestone and granite is utilized. Asphalt mixture is mixed at
temperature of 160°C and compacted at 150°C. Service characteristics of RPMS
incorporated asphalt mixture resulted higher Workability Index (WI) and lower
Compactability Energy Index (CEI) than control. Unconditional 0.5% RPMS asphalt
mixture led to comparable Indirect Tensile Strength (ITS) with control, yet having
poor moisture resistance with low Indirect Tensile Strength Ratio (ITSR). RPMS
resulted in higher resilient modulus and Leutner shear, while having comparable
dynamic creep performance than control asphalt mixture. Scanning Electron
Microscope (SEM) illustrated the fibrous and porous surface morphology of RPMS.
X-Ray Diffraction (XRD) shown RPMS mineralogical composition which contains
calcite, promoting good bitumen-aggregate adhesion. However, RPMS contained
high water solubility mineralogical compounds namely anhydrite, halite, sylvine,
quart and periclase. Chemical composition are determined via X-Ray Fluorescence
(XRF) indicating RPMS contained similar Portland cement composition namely SiO2,
Al2O3, K2O and CaO even after Loss On Ignition (LOI) of 52.5%. Toxicity
Characterization Leaching Procedure (TCLP) proved only Arsenic heavy metal is
detected with levels far below regulatory limits on raw RPMS. While RPMS
incorporated asphalt binder indicated a reduction in Arsenic proving good asphalt
binder integration. Non heavy metal elements which have agronomic application
namely calcium, iron & magnesium are detected. Thus proving RPMS is not harmful
to the environment. This research acts as a stimulus to incorporate RPMS in eco and
sustainable asphalt pavement development while providing industries with a greener
disposal alternative.